A proof of Connelly's conjecture on 3-connected circuits of the rigidity matroid

  • Authors:
  • Alex R. Berg;Tibor Jordán

  • Affiliations:
  • BRICS (Basic Research in Computer Science, Centre of the Danish National Research Foundation), University of Aarhus, Ny Munkegade, building 540, Aarhus C, Denmark;Department of Operations Research, Eötvös University, Pázmány Péter sétány 1/C, 1117 Budapest, Hungary

  • Venue:
  • Journal of Combinatorial Theory Series B
  • Year:
  • 2003

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Abstract

A graph G = (V , E) is called a generic circuit if |E| = 2|V| - 2 and every X ⊂ V with 2 ≥ |X| ≥ |V| - 1 satisfies i(X) ≤ 2|X| - 3. Here i(X) denotes the number of edges induced by X. The operation extension subdivides an edge uw of a graph by a new vertex v and adds a new edge vz for some vertex z ≠ u, w. Connelly conjectured that every 3-connected generic circuit can be obtained from K4 by a sequence of extensions. We prove this conjecture. As a corollary, we also obtain a special case of a conjecture of Hendrickson on generically globally rigid graphs.